<div class="problemindexholder" problemindex="A">
 <div class="ttypography">
  <div class="problem-statement">
   <div class="header">
    <div class="title">
     A. Generous Kefa
    </div>
    <div class="time-limit">
     <div class="property-title">
      time limit per test
     </div>
     2 seconds
    </div>
    <div class="memory-limit">
     <div class="property-title">
      memory limit per test
     </div>
     256 megabytes
    </div>
    <div class="input-file">
     <div class="property-title">
      input
     </div>
     standard input
    </div>
    <div class="output-file">
     <div class="property-title">
      output
     </div>
     standard output
    </div>
   </div>
   <div>
    <p>
     One day Kefa found
     <span class="tex-span">
      <i>
       n
      </i>
     </span>
     baloons. For convenience, we denote color of
     <span class="tex-span">
      <i>
       i
      </i>
     </span>
     -th baloon as
     <span class="tex-span">
      <i>
       s
      </i>
      <sub class="lower-index">
       <i>
        i
       </i>
      </sub>
     </span>
     — lowercase letter of the Latin alphabet. Also Kefa has
     <span class="tex-span">
      <i>
       k
      </i>
     </span>
     friends. Friend will be upset, If he get two baloons of the same color. Kefa want to give out
     <span class="tex-font-style-bf">
      all
     </span>
     baloons to his friends. Help Kefa to find out, can he give out all his baloons, such that no one of his friens will be upset — print «
     <span class="tex-font-style-tt">
      YES
     </span>
     », if he can, and «
     <span class="tex-font-style-tt">
      NO
     </span>
     », otherwise. Note, that Kefa's friend will not upset, if he doesn't get baloons at all.
    </p>
   </div>
   <div class="input-specification">
    <div class="section-title">
     Input
    </div>
    <p>
     The first line contains two integers
     <span class="tex-span">
      <i>
       n
      </i>
     </span>
     and
     <span class="tex-span">
      <i>
       k
      </i>
     </span>
     (
     <span class="tex-span">
      1 ≤
      <i>
       n
      </i>
      ,
      <i>
       k
      </i>
      ≤ 100
     </span>
     ) — the number of baloons and friends.
    </p>
    <p>
     Next line contains string
     <span class="tex-span">
      <i>
       s
      </i>
     </span>
     — colors of baloons.
    </p>
   </div>
   <div class="output-specification">
    <div class="section-title">
     Output
    </div>
    <p>
     Answer to the task — «
     <span class="tex-font-style-tt">
      YES
     </span>
     » or «
     <span class="tex-font-style-tt">
      NO
     </span>
     » in a single line.
    </p>
    <p>
     You can choose the case (lower or upper) for each letter arbitrary.
    </p>
   </div>
   <div class="sample-tests">
    <div class="section-title">
     Examples
    </div>
    <div class="sample-test">
     <div class="input">
      <div class="title">
       Input
      </div>
      <pre>4 2<br/>aabb<br/></pre>
     </div>
     <div class="output">
      <div class="title">
       Output
      </div>
      <pre>YES<br/></pre>
     </div>
     <div class="input">
      <div class="title">
       Input
      </div>
      <pre>6 3<br/>aacaab<br/></pre>
     </div>
     <div class="output">
      <div class="title">
       Output
      </div>
      <pre>NO<br/></pre>
     </div>
    </div>
   </div>
   <div class="note">
    <div class="section-title">
     Note
    </div>
    <p>
     In the first sample Kefa can give
     <span class="tex-span">
      1
     </span>
     -st and
     <span class="tex-span">
      3
     </span>
     -rd baloon to the first friend, and
     <span class="tex-span">
      2
     </span>
     -nd and
     <span class="tex-span">
      4
     </span>
     -th to the second.
    </p>
    <p>
     In the second sample Kefa needs to give to all his friends baloons of color
     <span class="tex-font-style-it">
      a
     </span>
     , but one baloon will stay, thats why answer is «
     <span class="tex-font-style-tt">
      NO
     </span>
     ».
    </p>
   </div>
  </div>
  <p>
  </p>
 </div>
</div>
